I noticed that there was some sandstone interval contains some considerable amount of Siderite. I know that this is diagenetic. Could we attribute some specific depositional environment to these sandstones with some initial specific mineralogical &/or chemical composition that led to the transformation to siderite in time. ???
The best known Fe carbonate is siderite (the stochiometric Fe content
is 48.2% Fe). This amount will rarely be attained in an ore deposit because
Fe carbonates tend to have a wide range of substitution of Mn, Mg, Ca for
bivalent Fe. Spherosiderite is microcrystalline siderite found in claystones
and coaly sandstones associated with coal seams (claybands and
blackbands). Ankerite (26% Fe) is ferroan dolomite which forms part of vein and replacement deposits, but occurs seldom in the above strongly reducing environments.
There exist a classical transformation with increasing Eh: Vivianite (blue iron Fe phosphate) – siderite (white iron) -goethite (brown iron ore). In SEDEX deposits there exists a facies differentiation dependent
mainly on the Eh and pH conditions occurring within the basin changing from calcareous hematite, magnetite, siderite to siliceous Fe ore or even pyrite (melnikovite) ore.
One should keep always in mind whether it is true sedimentary environment like the clay- and black bands which reflect lacustrine, paludal (swamp) or marsh-like (paralic) environments or a volcanic or hydrothermal influence is identified. In the latter case the situation may be a bit more complicated.
HGD
Dear Wael Alouani,
I want to propose two possibilities of siderite formation into sedimentary deposits (diagenetic and hydrotheral-metasomatic environments). My article as enclosed, second you can find:
Article A study of iron carbonates and clay minerals for understandi...
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M. T. Krupenin, thanks a lot, you really got my point and straight to the question.
Hechmi Garnit thanks a lot for your answer. Actually, yes, some of Ordovician reservoirs are rich in siderite.
In the study in which I was involved, the siderite concentration was seen in the Silurian reservoirs (esp, Acacus A interval). there is a huge variation in the concentration of such mineral from well to the other in in a short distance does not exceed 10 km at the same levels, the base of this reservoir layer.
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